The focusing of a luminous beam into different given ranges of a volume, this is both in a lateral and/or transversal direction to the luminous beam as well as in a parallel direction to the luminous beam, which plays an important role in a series of optical devices and/or with a set of optical procedures. From now on, as luminous beams must be conceived in particular laser beams delivered by a laser.
For example, laser beams are used in ophthalmology, in order to correct defective vision of a human eye by a laser-surgical intervention over the cornea of the eye. A special importance has the well-known procedure known as “LASIK” (laser in situ keratomileusis), in which by means of a pulsed laser beam material is removed not from the surface of the cornea, but from inside the cornea. This way, an external surface area of the cornea forms a fold-like cover also known as a “flap”, whose thickness is substantially smaller than the one of the cornea. This cover is folded away for the actual removal treatment, whereupon a given amount of material is removed through the area of the opened region by means of a pulsed laser beam, with which the defective vision is corrected. Afterwards the cover is folded back on the opened surface.
In order to be able to cut the cover in the cornea to the exact defined depth as carefully and precisely as possible, femtosecond laser pulses may be used—this is, laser pulses with suggested pulse-widths lower than 10−12 s. By means of such pulses, optical openings—which are also denominated “photo-disruptions”, which are locally limited and show an expansion of only a few micrometers—can be produced in the cornea. By placing several of these optical openings very close in exact given places, the cover can be formed very accurately. Thereby, a fundamental condition for the exact formation of the cover is the accurate positioning of the focus of the used pulsed laser beam, not only in the lateral direction, but most of all also in the depth of the cornea and thus in the propagation direction of the laser beam.
US 2003/0053219 A1 describes a zoom lens system which is intended for surgical applications. A zoom lens is moved in the direction of the laser beam for focusing into different depths, whereby the focal length of the focusing optics is modified. In order to be able to place the focus in the depth with the required accuracy, the zoom lens must be adjusted with a very high accuracy, which requires accordingly complex mechanics.
U.S. Pat. No. 6,751,033 B2 shows an ophthalmologic laser system, in which a laser beam delivered by a laser source is diverted in a lateral direction and thereafter is focused in a given depth by using optics with variable focal length. The same disadvantages of the system described in US 2003/0053219 A1 can be expected with this system.
A further application area for scanning devices of the above mentioned type are those denominated confocal laser scanning microscopes, in which a laser beam is focused on a given range of the volume of the object to be examined. The light emitted from this area is aimed over a detector in which a fine aperture is located over an intermediate image plane, which basically only allows the light emitted from the range and/or focus to pass, fading out the light from neighboring regions so that a dissolving takes place in the lateral and depth directions. A three-dimensional volume of the object which is being examined can be shown by the relative motion between specimen and focus in lateral direction and in the direction of the laser beam. The specimen table which holds the object is moved by positioning the focus in the direction of the laser beam relative to the object, is also mechanically complex and due to the relatively large mass of the sample table, does not allow a very fast adjustment.
The basic purpose of the concerned invention is to create a scanning device for focusing a luminous beam into determined ranges of a given volume by means of a simple laser beam, in a simple and exact way in the lateral direction and in the direction of the laser beam into different specific ranges of a volume, that can be focused following a determined procedure.